Fixed Fractional vs Fixed Lot: Which Sizing Really Compounds?

You multiply your account on paper. The curve in the backtest looks like a ski slope. Then you trade it fixed 0.10 lots and the equity just… drifts sideways.

This is a plain-English guide to fixed fractional vs fixed lot.

Same entries. Same exits. Same system. Different sizing.

This is where the fixed fractional vs fixed lot argument stops being theory and starts being money left on the table.

Why most traders quietly trade like a salary, not like equity

Most retail accounts run fixed lots without thinking about it.

"I trade 0.10 on this system" sounds normal, like choosing shoe size.

The problem is that fixed lot position sizing behaves like a fixed salary: whether your account is £2,000 or £20,000, the trade size doesn’t care, so the percentage impact on your equity is completely different.

That feels safe, until you realise it also quietly caps any compounding.

Fixed fractional vs fixed lot: the core difference

Let’s define this properly, in trader language, not exam language.

Fixed lot: you trade the same absolute size every time. 0.10 lots on EURUSD, every trade, win or lose, account up or down.

Fixed fractional: you risk a fixed percentage of current equity per trade — say 1% — then calculate lots from the stop distance so that if the stop is hit, you lose about 1% of the account, whatever size it is that day.

One of these lets equity growth scale your bet. The other pretends yesterday didn’t happen.

What actually compounds (and what just looks busy)

Take a very simple system, purely hypothetical:

• Expectancy: +0.5R per trade (average win bigger than average loss, or win rate > 50% at 1:1 R)
• 100 trades per year
• Starting equity: £10,000

Under fixed fractional at 1% risk per trade, your average trade is +0.5R × 1% = +0.5% of equity.

That’s percentage return on a changing base.

The maths looks like compound interest: Equityt+1 = Equityt × (1 + 0.005) on average.

Over 100 trades, you’re applying that expected 0.5% to a gradually growing number.

That’s compounding.

Now do fixed lot with the same 1% of starting equity as your reference.

You risk £100 per trade (1% of the original £10,000). That’s your R.

Average expectation per trade: +0.5R × £100 = +£50, regardless of current equity.

You’ve turned a percentage edge into a fixed cash edge.

At trade 1, +£50 is +0.5% of equity. At trade 100, if you’ve grown to £15,000, it’s only +0.33%.

The system is working just as well. You’ve simply throttled its growth.

Three trades that show the whole story

Same system. Same R-multiples. Different sizing.

After three trades with the same R outcomes, the equity lines have already diverged.

It’s tiny at three trades. It is not tiny at 300.

Losses: where fixed fractional quietly saves you

Most people focus on compounding the wins.

The more important bit is shrinking the losses.

Imagine ten straight losing trades at -1R each.

• Fixed fractional, 1% risk: you don’t lose 10% of the starting account; you lose 1% of a shrinking equity line each time.
• Fixed lot, £100 per R: you lose the full £100 ten times, whatever the drawdown.

On fixed fractional, those ten losses might cost you about 9.6% instead of 10% because each 1% is on a lower base.

On fixed lot, they cost exactly £1,000, whether you’re at £10,000 or halfway down a hole.

Mathematically, both are simple.

Psychologically, one of them feels like the brakes still work.

Why fixed lot feels safer (and why that feeling is wrong)

Fixed lot feels stable.

Same lot size, same stop distance, same money at risk.

Your brain likes constants, especially when you’re watching P&L flicker; it’s the same reason people love the neat numbers in that old martingale story, right up until they meet a real streak.

The problem is that markets don’t care about your preference for neatness.

Equity is dynamic, so using a static lot size is a mismatch between risk and reality.

As your account drops, fixed lot increases your risk as a percentage of equity.

At £10,000, a £100 loss is 1%.

At £7,000, the same £100 is 1.43%.

Same system, same trade, but your real risk has drifted up nearly 50% because you were too lazy to update the sizing formula.

As your account grows, fixed lot does the opposite.

At £20,000, £100 is only 0.5%.

You’ve halved your risk and halved your return expectation without changing a single line of code or a single rule.

So fixed lot is not safer.

It’s just less honest about what you’re actually doing.

Fixed fractional vs fixed lot in a positive expectancy system

Assume a hypothetical strategy:

• Expectancy: +0.4R per trade
• Standard deviation: 1.5R per trade (decent volatility)
• Trades: 500 over its lifetime before decay sets in

On fixed fractional, risk per trade is a constant percentage — say 0.75% of current equity.

Your expected return per trade is +0.4 × 0.75% = +0.3% of equity.

Over 500 trades, ignoring noise and compounding for a second, that’s an expectation of around +150% cumulative on the starting equity.

But because it compounds, the true expectation on the final number is higher than that simplistic 500 × 0.3%.

On fixed lot, using £75 as 0.75% of starting equity, your expectation per trade is £30.

Over 500 trades, that’s £15,000 total expected profit… whether your account is sitting at £3,000 after a drawdown or £40,000 after a run.

The curve you thought would bend upwards like a good compound curve instead looks suspiciously linear.

That’s not the market shafting you.

That’s position sizing flattening your edge.

Where fixed lot sizing still makes sense

Fixed fractional is not holy scripture.

There are cases where fixed lot is actually rational.

• Very small accounts near minimum lot sizes, especially in instruments like gold (XAUUSD) where 0.01 is the floor and the monetary swings are big.
• Situations where your real risk is account-independent — for example, using the account as margin for a completely external risk budget.
• Testing a new system with "token" size where the point is psychological exposure, not compounding.

If you’re trading XAUUSD with a 0.01 lot minimum on a tiny account, fixed fractional maths might tell you to risk 0.003 lots.

You can’t.

So you either don’t trade that system on that account, or you accept that you’re running effectively fixed lot until the equity is big enough for the fraction to matter.

This is where people say "the maths doesn’t work on small accounts".

The maths works fine.

The brokerage constraints don’t.

How automation changes the fixed fractional vs fixed lot decision

Automation doesn’t change the underlying maths.

It just makes whatever you decide happen every time, without that 2am "shall I round it up" moment.

If you run multiple systems — FX, indices, gold — the real question is not "fixed fractional vs fixed lot" in isolation.

It’s "fractional of what".

Total equity across all systems?

Per-system sub-account?

One system at 0.5% per trade and another at 1.5% quickly turns into a mess if you’re also manually changing lot sizes.

Automating fixed fractional sizing lets you say "this strategy gets 0.75% per trade" and then forget about the arithmetic.

Automating fixed lot just means you execute the same flawed scaling very efficiently.

Fast and wrong is still wrong.

Position sizing, risk of ruin, and your actual edge

All of this sits on top of your system’s expectancy, not instead of it.

If expectancy is negative, fixed fractional just compounds the problem slightly more elegantly.

This is why position sizing belongs in the same conversation as risk of ruin and drawdown, not "how to squeeze out more return" on a bad strategy.

We’ve already gone through the mechanics of how much to risk per trade in detail here: /blog/how-much-should-you-risk-per-trade-without-blowing-up.

Fixed fractional makes that risk choice stick.

Fixed lot quietly changes the real percentage exposure as your equity moves.

So you can have a nicely optimised system with a good Sharpe, and then sabotage it with static lot sizes; we’ve covered the Sharpe ratio illusions in /blog/what-is-sharpe-ratio-trading-and-where-it-misleads-3.

The numbers on the report only mean anything if the sizing logic that generated them is the sizing logic you actually trade.

The drawdown picture: same system, different pain

Think about your worst historical run.

Say your backtest shows a maximum drawdown of -20R.

On fixed fractional at 1% risk, that’s about a 20% drawdown, give or take the slight cushioning from the shrinking equity base.

On fixed lot using 1% of the starting equity as your R, the same -20R is exactly -20% in cash terms.

But notice what’s happening.

At the bottom of the drawdown, you are now risking more than 1% of current equity per trade, because you’re still putting £100 at risk on a smaller account.

If you chose 1% because your psychology and ruin maths could just about stomach the 20% drawdown, you are now quietly operating at a higher effective risk level just when you’re most vulnerable.

Fixed fractional leans the other way.

By the bottom of the drawdown your pound amount per trade is lower, so effective risk stays at 1% of that smaller equity.

Same system. Same worst run in R.

Very different behaviour at the point your brain wants to hit the eject button — a point we’ve looked at in depth in /blog/why-traders-abandon-winning-systems-at-the-worst-time.

So what should you actually do on Monday?

First, forget the labels for a moment.

Ask one clean question: "When my equity changes, do I want my percentage risk per trade to stay the same, go up, or go down?"

If the answer is "stay the same", you’ve just chosen fixed fractional sizing whether you like the name or not.

Then write it down as a rule:

• Decide a risk percentage per trade for each system (often somewhere in the 0.25%–1.5% range, depending on edge and volatility).
• Calculate lot size from stop distance and current equity on every trade.
• Do not override the calculation because "0.13 lots looks weird".

If you truly have a reason to use fixed lot on a particular account — minimum lot constraints, or a deliberate choice to cap monetary swings — then be honest about what you are giving up in compounding and in risk control.

But stop pretending that fixed lot is "the same thing" with less faff.

It’s not.

It’s a different risk profile that happens to be easier to type into a ticket.

Trading involves real risk of loss. No position sizing method removes the possibility of losing money.

Start your free 14-day ArcisTrade demo →

If you’re going to test fixed fractional sizing, it helps when the lot maths and execution are handled for you.

P.S. Watch how your position size breathes with equity across systems — FX, indices, gold — then decide whether you ever want to go back to static lots.